In their most basic construct, bones are formed of a relatively soft, spongy cancellous bone having a high degree of visible porosity, which is surrounded by a much more rigid and dense material called the cortex, or cortical bone. The cancellous bone yields under relatively low loading, while the much denser cortical bone supports much higher loading.
One of the most heavily-stressed, load-carrying bone joints in the human body is the hip joint. The hip joint is essentially a ball and socket mechanism formed between the pelvic bone and the proximal end of the femur. The femur, otherwise known as the thigh bone, generally comprises an elongate shaft extending from the pelvis to the knee. The proximal end of the femur includes a head, a neck and greater and lesser trochanter regions that connect the femoral head and neck to the shaft of the femur, as shown in FIG. 1. Generally speaking, the trochanter region holds the femoral head and neck at an angle of about 130 degrees relative to the femur shaft.
While the femur is generally reputed to be the longest and strongest bone in the human skeleton, the proximal end of the femur is particularly susceptible to the onset of osteoporosis, which severely compromises the strength of the hip joint. Osteoporosis is a metabolic disease characterized by a decrease in bone mass and bone structure impairment and, leads to skeletal fractures under light to moderate trauma and, in its advanced state, can lead to fractures under normal physiologic loading conditions. Common fracture sites include the hip, wrist and vertebrae. Hip fractures generally occur in one of two primary areas—the femoral neck or the trochanter regions. Common fractures in the femoral neck and the trochanter regions include subcapital neck fractures, transcervical neck fractures, intertrochanteric neck fractures, subtrochanteric neck fractures, greater trochanter fractures and lesser trochanter fractures, as shown in FIG. 2.
While osteoporosis can affect persons of all ages and regardless of gender, it is especially prevalent in the elderly population. Femoral neck fractures are a major source of morbidity and mortality in elders. A very high percentage of all hip fractures occur in people over the age of fifty. During the aging process, in general, endosteal and outer periosteal diameters increase as a protective mechanism. As the bone mass shifts further from the epicenter, skeletal strength is maximized despite a decrease in bone mass. Similar protective mechanisms, however, do not occur in areas of cancellous bone, such as in the femoral neck. Because the femoral neck naturally has low levels of periosteum, this area of the femur is unable to compensate for the loss of endosteal bone by periosteal bone formation. When an elderly patient falls, some amount of energy is dissipated. Most of the energy in a fall is absorbed by active muscle contractions. However, in an elderly patient, the neuromuscular response often cannot act quickly enough to dissipate this kinetic energy and, instead, it gets transferred to the femoral neck. Consequently, because the femoral neck can only absorb a portion of that energy, the level of stored energy in the femoral neck often exceeds its threshold when an elderly person falls and a fracture develops.
While the femoral neck clearly poses a difficult problem to the elderly patient, it also poses a significant challenge to orthopedic surgeons and others skilled in the art seeking to mitigate the number of such occurrences and subsequent hospitalizations. Due to an increase in the elderly population, the number of cases and hospitalizations has been exacerbated. As a result, medical costs from such hip fractures place a significant strain on what many consider to be an already over-extended healthcare system.
Prior art devices and procedures relating to hip fractures generally focus on repairing hip fractures by reducing, compressing and stabilizing the cracked or broken portion of the bone. Traditional devices for treating a hip fracture comprise an intramedullary nail positioned within the intramedullary canal of the femur and configured for mechanical connection with a hip screw oriented in a position that is substantially parallel to the longitudinal axis of the femoral neck. One or more external plates are also often added for additional support and stability. Exemplary configurations are disclosed in U.S. Pat. No. 5,531,748 to de la Caffinierre, U.S. Pat. No. 6,443,954 to Bramlet et al., U.S. Pat. No. 6,511,481 to von Hoffmann et al., U.S. Pat. No. 6,562,042 to Nelson and U.S. Pat. No. 6,855,146 to Frigg et al. Some conventional designs may also inject a flowable material, such as bone cement, to further stabilize the device within the bone, as discussed in U.S. Pat. No. 7,488,320 to Middleton.
Surprisingly, however, few attempts have been made to develop devices and methods aimed at preventing hip fractures from occurring in the first place. There exist no standard procedures employed by doctors and others skilled in the art for augmenting the femoral neck to guard against future trauma to the hip joint. Over the past 50 years, very few investigations into prophylactic strengthening of an intact femoral neck have been reported. In 1960, G. S. Crockett suggested positioning a single pin in the femoral neck to strengthen the neck axis against shear stresses. In 2001, Franz et al. investigated the augmentation effects of injecting low-viscosity bone cement into the proximal end of the femur. Most recently, U.S. Pat. No. 6,679,890 to Marguiles et al. has disclosed a “hybrid technique” that uses a single implant component in combination with cement injection. The '890 patent inserts a hollow implant into the femur along the longitudinal axis of the femoral neck and thereafter fills the implant and the surrounding bone with cement. The “hybrid technique” of the '890 patent focuses on using bone cement to form a union between a single implant component and surrounding cancellous bone.
Accordingly, there currently exist no devices, methods or systems in the prior art directed to the prophylactic strengthening of an intact bone, such as the femur and particularly the femoral neck, using multiple supporting and augmentative implant components and which does not require the use of a flowable material.